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(11) | EP 4 270 021 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | DEVICE AND METHOD FOR MEASURING A RESISTANCE VALUE OF A RESISTOR OF A SAFETY DEVICE OF AN ELECTRIC OR HYBRID VEHICLE |
| (57) Method of measuring a resistance value of a resistor (PTC) of a safety device for
electric or hybrid vehicles arranged to discharge a capacitive electric energy of
a vehicular electric network, in the event of an accident, the method including the
procedure of triggering a electric discharge through said resistor and to calculate
(Step 5) said electric resistance value as the ratio between an initial voltage value,
measured before the start of the electric discharge, and an initial current value
equal to an average value of the discharge current multiplied by the factor approximately
5.
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Field of the invention
[0001] The present invention relates to the field of methods for measuring a power resistance in safety devices of electric or hybrid vehicles. In which the safety devices are arranged to discharge a capacitive electric energy, stored in the vehicular electric network, in the event of an accident.
State of the art
[0002] ISO 26262, entitled "Road vehicles - Functional safety", is an international standard for the functional safety of electrical and/or electronic systems installed in production road vehicles, defined by the International Organization for Standardization (ISO) in 2011, and revised in 2018.
[0003] According to the risk analysis and assessment performed on the basis of the ISO 26262 standard, a safety mechanism is required to discharge the residual electrical capacity of the propulsion mains after disconnecting the propulsion batteries in emergency situations such as of an accident and in general for emergency situations which could result in an electric shock.
[0006] It is, in fact, known that the resistance value tends to increase with the aging of the components. This can lead to discharge times of the residual capacity of the vehicular electrical network, which are not compatible with the above mentioned standard.
[0007] In the automotive field, the processing units that supervise the monitoring and control of a vehicle are equipped with data interfaces and processing units that have analog interfaces such as to perform the aforementioned measurements of the resistance value and with galvanic isolation of such interfaces.
[0008] The sensors on board of the vehicle are therefore arranged to communicate with the processing unit via the vehicle data network with intrinsic peculiarities of each sensor. For example, voltage sensors have a sampling frequency of the order of 30 ms, while current sensors have a sampling frequency of the order of 10 ms, therefore it is difficult to obtain simultaneous voltage and current measurements.
[0009] In fact, the measurements must be performed during the discharge of the residual capacity, preferably at the beginning of it, with voltage and current values that vary over time.
[0010] To these uncertainties must also be added the uncertainties deriving from the transmission time of the data packets containing the voltage and current measurements, along the vehicular data network.
[0011] Therefore, currently, the only possible solution is to perform dedicated measurements using an external measuring device equipped with appropriate voltage and current sensors, in order to calculate the resistance value as the ratio between voltage and current.
[0012] According to a safety device produced by the present Applicant, the number of resistors is relatively high to have a sufficient degree of redundancy and to distribute any current peaks.
[0013] Evidently, the fact that a single safety device is equipped with a large number of resistors further complicates the problem of monitoring each resistor, independently of the others, so as to promptly intervene with its replacement.
[0014] Unless specifically excluded in the detailed description that follows, what is described in this chapter is to be considered as an integral part of the detailed description.
Summary of the invention
[0015] The object of the present invention is to propose a device and method for measuring the power resistance of an electric or hybrid vehicle.
[0016] The technical problem arises specifically in the automotive field, in which the processing unit responsible for monitoring and controlling vehicle functions is not equipped with analog interfaces with galvanic isolation but only with data interfaces. Therefore, measurement information circulates over a vehicular data network.
[0017] The basic idea of the present invention is to carry out the measurement of the initial voltage, before the activation of the discharge of the residual capacity and to average the current values for a time interval between the start of the discharge and the achievement of a preordained voltage threshold. Subsequently, the initial value of the discharge current is calculated by multiplying said average value by 5, then the resistance value is calculated as the ratio between the initial voltage and the initial current.
[0018] Evidently, the voltage is measured across the resistor, while the measured current flows through the resistor.
[0019] Advantageously, it is possible to obtain an estimate of the resistance value of the resistor, with a much better precision than the tolerances of the resistor itself.
[0020] The dependent claims describe preferred variants of the invention, forming an integral part of the present description.
Brief description of the figures
[0021] Further objects and advantages of the present invention will become clear from the detailed description that follows of an embodiment of the same (and of its variants) and from the annexed drawings given for purely explanatory and non-limiting purposes, in which:
Fig. 1 shows an equivalent electric circuit diagram for measuring a resistance value of a resistor of a safety device for discharging the capacitive currents stored in a vehicular electric network;
Fig. 2 shows the voltage and discharge current diagrams;
Fig. 3 shows an example of a flow diagram of the method object of the present invention.
[0022] The same reference numbers and letters in the figures identify the same elements or components or functions.
[0023] It should also be noted that the terms "first", "second", "third", "superior", "inferior" and the like may be used herein to distinguish various elements. These terms do not imply a spatial, sequential, or hierarchical order for the modified items unless specifically indicated or inferred from the text.
[0024] The elements and characteristics illustrated in the various preferred embodiments, including the drawings, can be combined with each other without however departing from the scope of protection of the present application as described below.
Detailed description
[0025] Fig. 1 shows an example of an electromechanical layout of a safety device DEV for discharging the residual currents stored in the vehicular electric circuit C, which is schematized as a capacitor.
[0026] The resistor PTC is indicated with the abbreviation of a Positive Temperature Coefficient, generally indicated with the abbreviation PTC. However, it may also not be Positive Temperature Coefficient resistor.
[0027] The processing unit VCU is arranged to control the discharge switch SW and to acquire information about voltage and current measurements by means of the sensors V and A respectively, through the vehicular data network.
[0028] Therefore, the sensors are connected to the processing unit via a vehicular data network, for example, of the CAN or LIN type.
[0029] With reference to Fig. 2, two simultaneous time diagrams are shown, respectively representative of voltage and discharge current.
[0030] On the voltage and current graphs representative of a discharge procedure, black dots are arranged. These black dots indicate the sampling time positions of voltage and current respectively and for this reason the relative offset with respect to the ordinate axis is indicated with question marks, as it is not possible to know exactly when these samples are acquired and therefore, it is not possible to calculate the resistance value as a ratio of simultaneous pairs of voltage and current values.
[0031] With reference to figure 3, according to the present method the following steps are performed in succession:
- (Step 1) Acquisition of an initial voltage measurement while the switch SW is open, i.e. the electric circuit is isolated,
- (Step 2) Closing of the switch SW and simultaneous measurement of the discharge current and of the voltage across the resistor, until the measured value of the voltage exceeds (">") said preordained threshold (S),
- (Step 3) detection of the instant in which the measured voltage value becomes lower ("<") than the aforementioned threshold, then
- (Step 4) Calculation of the average of the acquired current values and calculation of the initial current of the discharge as the product of the average of the current values by 5,
- (Step 5) Calculation of the resistance value as the ratio between the initial voltage value and the initial current value.
[0032] The VCU, thanks to the present invention, is able to monitor any aging of the discharge resistances by appropriately signalling the need for maintenance of the safety system.
[0033] The electrical network discharge procedure and the contextual measurement of the resistance value of the resistor PTC can be planned according to predetermined time intervals.
[0034] The present invention is inspired by the fact that the law governing the discharge current is given by
[0035] Furthermore, the value of the average current I is given by the integral between 0 and 5tau divided by this time interval. From which it can be deduced that the average current during the discharge multiplied by a factor of about 5 leads to the initial current value sought to evaluate the V/I ratio. The exact value of the factor is equal to 5.035, however it is believed that there is no particular advantage in using the exact value rather than its approximation 5.00.
[0036] It is interesting to note that the initial voltage value can be measured before closing the switch SW and therefore, its measurement can be uncorrelated from the current measurements performed during the discharge of the vehicular electric circuit C.
[0037] With regard to step 3 of comparing the voltage value measured with the threshold S, it provides that as long as the voltage value measured exceeds the threshold S, then the loop closes on step 2, therefore, the switch SW is kept closed and the sampling of the measured voltage and current values is continued.
[0038] According to a preferred variant of the invention in step 3, the samples of the measured current are rejected if they are lower than a predetermined current threshold, selected taking into account the precision of the implemented current sensor.
[0039] For example, the switch can be opened after calculating the resistance value in Step 5 or within step 4.
[0040] The different samples acquired during the discharge, with a sampling step of 10 ms for example, each represents an average value within the sampling interval.
[0042] Alternatively, a moving average can be performed and the calculated value of the moving average can be acquired at the instant in which the measured voltage value becomes lower than the aforementioned threshold S.
[0043] The value of the threshold S is preferably equal to 0.007 multiplied by the value of the initial voltage.
[0044] The processing unit is configured to command the discharge of the propulsion electric network capacity following the detection of an impact and/or vehicle overturning. Such events, for the purposes of the present invention are referred to generically as an "accident".
[0045] The present invention can advantageously be implemented through a computer program comprising coding means for carrying out one or more steps of the method, when this program is executed on a computer. Therefore it is understood that the scope of protection extends to said computer program and also to computer-readable means comprising a recorded message, said computer-readable means comprising program coding means for carrying out one or more steps of the method, when said program is run on a computer.
1. Method of measuring a resistance value of a resistor (PTC) of a safety device for
electric or hybrid vehicles arranged to discharge a capacitive electric energy of
a vehicular electric network, in the event of an accident, the method comprising the
procedure of trigger an electric discharge through said resistor and to calculate
(Step 5) said electric resistance value as the ratio between an initial voltage value,
measured before the triggering of the electric discharge, and an estimated initial
current value equal to an average value of the discharge current multiplied by a factor
equal to 5 or 5.035, wherein the average value of the current is calculated in a time
interval starting from an instant of the triggering of the electric discharge up to
an instant in which the voltage value is equal to 0.007 times said initial value.
2. Method according to claim 1, comprising the following steps in succession:
- (Step 1) Acquisition of said initial voltage measurement while the switch (SW) is open,
- (Step 2) Closing of the switch (SW) and simultaneous measurement of the discharge current and of the voltage across the resistor, until the measured value of the voltage exceeds (">") said preordained threshold (S),
- (Step 3) detection of the instant in which the measured voltage value becomes lower ("<") than the aforementioned threshold, then
- (Step 4) Calculation of the average of the acquired current values and calculation of the initial current of the discharge as the product of the average of the acquired current values by said factor.
3. Method according to any one of claims 1 or 2, wherein said average value of the discharge
current is calculated by means of a moving average.
4. A computer program comprising program coding means adapted to implement all steps
of any one of claims 1 to 3, when said program is run on a vehicle processing unit
(VCU) configured to control and monitor a device of safety for electric or hybrid
vehicles arranged to discharge a capacitive electric energy of a vehicular electric
network, in the event of an accident.
5. A computer readable means comprising a recorded program, said computer readable means
comprising a program coding means adapted to carry out all steps of any one of claims
1 to 3, when said program is run on a vehicular processing unit (VCU) configured to
control and monitor a safety device for electric or hybrid vehicles arranged to discharge
a capacitive electrical energy of a vehicular electrical network, in the event of
an accident.
6. A vehicular processing unit (VCU) configured to control an electric or hybrid vehicle
safety device arranged to discharge a capacitive electrical energy of a vehicular
electrical network, in the event of an accident, the processing unit being configured
to measure a value of electrical resistance of a resistor of said safety device by
triggering an electric discharge through said resistor and calculating said electrical
resistance value as the ratio between an initial voltage value, measured before the
triggering of the electric discharge, and an initial current value equal to an average
value of the discharge current multiplied by a factor equal to 5 or 5.035, in which
the average value of the current is calculated in a time interval starting from an
instant of the triggering of the electric discharge up to an instant in which the
value of the voltage is equal to 0.007 times said initial value.
7. Electric or hybrid vehicle comprising
- a vehicular electrical network,
- a vehicular data network,
- a safety device arranged for discharging a capacitive electric energy from the vehicular electrical network by means of at least one resistor (PTC), in the event of an accident, the device comprising a voltage sensor (V) and a current sensor (A) arranged to measure respectively a voltage across the at least one resistor and a discharge current flowing through said at least one resistor, and wherein said voltage and current sensors are operatively connected to said vehicular data network,
- a processing unit (VCU), operatively connected to said vehicular data network and arranged to cause an activation of said safety device,
and wherein said processing unit is in accordance with claim 6.